1. Field of the Invention
This invention relates to a structural element useful in aerospace applications, as well as a method of preparing such a structural element for use in aerospace applications, such as a structural element suitable as an aircraft component. In particular, in the present invention the structural element comprises a first member such as a face sheet, and at least one rib-receiving member integral to the first member, wherein the rib-receiving member comprises at least one rib-receiving element for receiving the rib member.
2. Background Information
Aircraft components including intake ducts, flooring and wing sections are often made of honeycomb material which is lightweight, rigid and capable of being fabricated in many shapes. Depending on the particular application, the use of such honeycomb material may be expensive, in terms of life cycle costs, and may require extensive maintenance and repair. In some circumstances, it is also not readily adaptable to the attachment of other components. This drawback may be overcome by reinforcing elements within the honeycomb, but this typically involves adding to the weight of the structural element and thus reducing the advantage of the low weight of the honeycomb material.
Furthermore, honeycomb core structures suffer from susceptibility to moisture intrusion resulting from their open-cell construction. Even non-visible face sheet damage can create a path for moisture intrusion. When moisture condenses on the outside of an aircraft wing skin fabricated with honeycomb core panels, the pressure differential between the sandwich interior and the atmosphere during descent can force moisture into the honeycomb core. Repeated freeze/thaw cycles are also known to cause corrosion of aluminum honeycomb cores, and delamination of the face sheet from the core. Repair complications due to honeycomb core water intrusion represent an additional difficulty.
Other problems with honeycomb core structures are the presence of undetected damage, cracked skins, poor radar transparency due to the metal foil and poor thermal insulation due to the conductivity of aluminum foil which is often a component of honeycomb structures.
In U.S. Pat. Nos. 5,273,806, 5,487,930, and 5,508,085, structural elements are disclosed which comprise two outer structures and an inner structure interposed between the two outer structures. The inner structure includes lateral and longitudinal ribs. The ribs may be bonded to the outer structures. Alternatively, the structures may be joined together by interlocking ribs and grooves. The grooves are typically formed on the inner surfaces of the outer structures to mate with the ribs of the inner structures. While the inner structures may be formed from metal or composite material, the outer structures are generally formed from metal with grooves machined into the metal structures. As a result, since the metal is typically more dense and less stiff than the composite material, the overall weight of the structural element increases while its stiffness is reduced.